1. Field of the invention
This invention relates to rollers for conveyor systems. In particular the present invention is a novel conveyor roller with frictional drive that minimizes the likelihood that the articles conveyed will be damaged as a result of accumulation.
2. Description Of The Related Art
Many different styles of conveyor roller systems have addressed the problem of product damage in the event of accumulation on the conveyor. The most popular of such systems is known as a line shaft conveyor. FIG. 1 illustrates one roller in a typical line shaft conveyor system. In an actual system, many such rollers are positioned adjacent each other in order to move the product along the conveyor system.
The line shaft conveyor system has two rails 12 that extend along the length of the system (normal to the plane of the page in FIG. 1). Extending between the rails 12 is stationary shaft 14. Roller 16 is mounted on shaft 14 by virtue of two bearing elements 18. Roller 16 is thus free to rotate about shaft 14. Line shaft 20 extends along the length of the conveyor system and is rotationally driven by the conveyor power source (not illustrated). Pulley 22 is slip-fitted on line shaft 20 and transmits rotation to roller 16 by virtue of belt 24. Groove 26 is formed in roller 16 so as to avoid interference between belt 24 and products to be conveyed.
In order to allow roller 16 to stop rotating when products accumulate, the force of stationary products on the conveyor that have accumulated exceeds this frictional force between pulley 22 and line shaft 20, there will be slippage at the interface between pulley 22 and line shaft 20. Accordingly, the rollers of the line shaft system will not rotate when accumulation occurs.
Several limitations of a line shaft conveyor system have become apparent. Because of its many moving parts, the line shaft system is difficult and expensive to maintain. Ball bearings utilized in this type of system are prone to failure. This is especially true in food and chemical application where fluids and particles may be present in the environment that clog or dry out the bearings of this type of system. In addition, belts may break or there may be a loss of driving force to the belts becoming stretched or greasy. Also, the frictional force between the pulley and line shaft remains constant, regardless of the weight of the article being conveyed. Therefore, the slippage does not occur at the correct time for all types of articles and damage may occur during accumulation of articles on the conveyor.
Many complex systems have been developed in an effort to overcome the shortcomings of the line shaft type system. In particular, systems utilizing ball clutches or plastic on plastic sliding surfaces have been proposed. These types of systems, however, are typically complex and expensive (ball clutch) or unable to carry adequate loads without undue wear (plastic on plastic sliding surfaces).